Process for sweetening a hydrocarbon oil with an alkanol amine, sodium plumibte sulfur and air



Oct. 9, 1956 M. L-KALINOW'SKI 2 766 180 PROCESS FOR SWEETENING A HYDROCARBON on WITH AN ALKAI,\IOL

AMINE, SODIUM PLUMBITE SULFUR AND AIR Filed June 16, 1955 JNVENTOR.

Mafliew L. Ka/inowsk/ ATTORNEY Unitfid States Patent PROCESS FOR SWEETENING A HYDROCARBON OIL WITH AN ALKANOL AMINE, SODIUM PLUMBITE SULFUR AND AIR Mathew L. Kalinowski, Chicago, EL, assignor to Standard Oil Company, Chicago, [1]., a corporation of Indiana Application June 16, 1953, Serial No. 361,944

Claims. (Cl. 196+29) This invention relates to the sweetening of sour hydrocarbon oils. More particularly the invention relates to an improvement in the sweetening of sour petroleum distillates by the doctor process.

Owing to the malodorous nature of the mercaptans present in most petroleum distillates, it is necessary to remove these compounds in order to obtain a salable material. Many methods are known for removing the mercaptan odor from mercaptan-containing distillates. These mercaptan-containing distillates are commonly known as sour distillates and the essentially mercaptanfree distillates are commonly known as sweet distillates. The more common processes in use in the petroleum industry convert the malodorous mercaptans to disulfides which are relatively innocuous with respect to odor.

The oldest and probably most common sweetening process now in use is the so-called doctor process wherein an aqueous caustic-sodium plumbite solution and free sulfur are used to convert the mercaptans to disulfides. The doctor process has many disadvantages which arise primarily from the formation of insoluble lead sulfide. Frequently extremely prolonged settling times are required to remove the PbS from the hydrocarbon oil.

Normally not only the doctor solution but also a blackstrap layer must be separated from the oil in order to get a PbS-free product oil. The black-strap layer which is a fairly stable emulsion of doctor solution, PbS and oil can be separated only by long settling times or by filtration. Some of the separation difliculties in the doctor process can be overcome by the use of free-sulfur in marked excess of the theoretical amount of 0.5 mol per mol of mercaptan sulfur present in the oil. The amount of excess sulfur used varies with the type of stock.

An additional problem in the use of the doctor process lies in the regeneration of the spent doctor solution for reuse in the process. The doctor solution must be regenerated in order to provide a commercially economic operation. Normally the spent doctor solution is regenerated by contact with free-oxygen at elevated temperatures, e. g., 200 to 300 F. The use of lower temperatures results in extremely long regeneration times.

A further disability of the doctor process lies in the fact that kerosenes and heater oils that have been doctor sweetened generally show an increase in burner deposits as compared with the sour oil.

Despite these disabilities the doctor process is used because for distillates boiling in the heavier-than-gasoline range it is often the only practical way to sweeten particular sour oils.

An object of the invention is to improve the sweetening of sour hydrocarbon oils by means of the doctor process. Another object is to improve the sweetening of sour. petroleum distillates which boil in the heavier-than-gasoline range, i. e., between about 325 and 650 F. Still ice another object is the sweetening of sour hydrocarbon oils by an improved doctor process wherein the spent doctor solution is regenerated at moderate temperatures in a reasonable time. A further object is the sweetening of sour hydrocarbon oils by an improved doctor process wherein the sweetening'reaction and the regeneration reaction are carried out substantially simultaneously. A particular object isthe sweetening of a sour heater oil by an improved doctor process wherein substantially simultaneous regeneration of the doctor solution and the sweetening of the oil takesplace and the conventional separate spent doctor regeneration procedure is eliminated. Other objects will become apparent in the course of the detailed description.

It has been found that spent doctor solution from the treatment of sour hydrocarbon oils can be readily regenerated by free-oxygen contacting at moderate temperatures, i. e., below about F. by having present in said spent doctor solution an effective amount of an alkanolamine containing from 2 to 3 carbon atoms in each alkyl group.

Further, it has been found that it is possible to eliminate the separate regeneration procedure of the conventional doctor process by using as the sweetening agent a doctor solution containing an effective amount of an alkanolamine containing from 2 to 3 carbon atoms in each alkyl group and contacting the free sulfur-sour oilagent mixture with free-oxygen for a time sufiicient not only to sweeten the sour oil but also to convert the PbS formed to water-soluble plumbite. At the end of this time the aqueous sweetening agent phase is separated from the sweet oil phase and is recycled to the sweetening zone.

The hydrocarbon oil feed to the process of this invention may be any liquid hydrocarbon oil containing detectable amounts of mercaptans, i. e., the oil should be sour to the conventional doctor test or should have a mercaptan number or copper number above about 1. The process is particularly suitable for the treatment of sour petroleum distillates boiling below about 750 F. Examples of these distillates are naphtha, kerosene, diesel oil, heater oil, gas oil, etc. The process may be used on distillates obtained by the fractional distillation of crude petroleum or on distillates obtained from various conversion processes such as thermal cracking, catalytic cracking, reforming in the presence of hydrogen, etc. Sour petroleum distillates boiling in the heavier-than-gasoline range, i. e., between about 325 and 650 F., e. g., a heater oil boiling between about 330 and 575 F. are a preferred feed.

The sweetening agent of this invention consists of a conventional doctor solution and a water-soluble aliphatic amine. The doctor solution is made up of an aqueous solution of an alkali metal hydroxide and the reaction product of litharge and the alkali metal hydroxide. The amount of free-alkali metal hydroxide present in the doctor solution may be between about 5 and 30 weight percent, usually between about 10 and 15%. The plumbite content is commonly given in terms of the percent of PbO theoretically present. This content for a fresh doctor solution is usually between about 1.5 and 2.5% based on aqueous caustic solution. However, it is to be understood that the process is operative with any range of doctor solution compositions that are operable in a conventional doctor process.

The preferred amines of this invention are the watersoluble alkanolamines. The term water soluble is intended to include those alkanolamines which are sufliciently soluble to have a beneficial effect. Preferably the alkanolamines should be soluble to the extent of at least about 2 volume percent based on doctor solution. The most suitable alkanolamines are those wherein not more than 3 carbon atoms are present in each alkyl group or, conversely, wherein each alkyl group contains from 2 to 3 carbon atoms. Examples of these alkanolamines are mono, diand triethanolamine and the propanolamines.

Other amines which are suitable for the purposes of this invention are: (a) alkanol diamines containing from 3 to carbon atoms such as propanol diamines and butanol diamincs; (b) alliandiolamines containing from 3 to 5 carbon atoms such as the propandiolarnines and pentandiolamines; and (c) alkandiamines containing from 2 to 3 carbon atoms such as ethylene diamine and trimethylene diamine.

For purposes of brevity the invention is described hereinafter in terms of the alkanolamines. The amount of alkanolamine present in the sweetening agent, i. e., the solution of doctor solution and alkanolamine must be at least enough to have an appreciable beneficial effect on the time of the PbS conversion. Generally beneficial effects are obtained when using amounts of alkanolamine as small as 0.5 volume percent. Larger amounts may be usei. e. g., as much as 50 volume percent; for reasons hereinatter explained, it is preferred to use between about 1 and 4%. The optimum usage of alkanolamine will vary with the type of sour distillate being charged.

It has been found that the alkanolamine effects the sweetening reaction and the conversion reaction, i. e., PbS piumbite, differently. That is, the presence of alkanolamine increases the rate at which the PbS is converted and decreases the rate of sweetening. Thus high concentrations of alkanolarnine in the sweetening agent result in relatively short PbS conversion time and, on the other hand, the sweetening time is shortened by maintaining a low concentration of alkanolamine in the sweetening agent. (Usually sweetening time in this process is somewhat longer than when using conventional doctor solution.) When a sour distillate boiling in the heavier-than-gasoline range is the feed to the process, a practical balance between the sweetening reaction and the PbS conversion reaction is obtained when using be tween about 1 and 4% of alkanolamine such as triethanolamine.

In order to obtain a sweet product it is necessary to have present in the agent-sour oil contacting zone freesulfur in an amount in excess of the theoretical. The theoretical quantity of free-sulfur needed for the sweetening reaction is 0.5 mol per each mol of mercaptan sulfur present in the sour oil. For some unknown reason the use of the theoretical quantity of free-sulfur does not produce an oil that is sweet to the doctor test. The amount of excess free-sulfur necessary varies with the sour oil charged and the operating conditions. In general the higher boiling the sour oil, the more excess sulfur that is needed to produce a sweet product. It has been found that in general the more excess sulfur present, the faster the rate of PbS conversion. However, the amount of sulfur present should be controlled to a level below that at which corrosive sulfur appears in the product oil, i. e., corrosive sulfur as determined by the copper strip test. Also, it has been found that the higher the concentration of alkanolamine, the greater the amount of excess sulfur that must be utilized in the process to obtain res'onable sweetening times, e. g., excess at 2% alkanolamine and 75% excess at 50% alkanolamine. In general the amount of sulfur added in excess of the theoretical amount (hereinafter referred to as a percentage of the theoretical quantity, e. g., 10% excess sulfur, is equal to 110% of the theoretical) may vary from 5% or less to as much as 100% or more. When operating on sour distillates boiling in the heavier-than-gasoline range it is preferred to use between about 10 and 30% excess free-sulfur.

In order to obtain the substantially simultaneous regeneration of the sweetening agent and the sweetening of the sour oil, it is necessary that free-oxygen be present in the contacting zone. The free-oxygen may be introduced in the form of a readily reducible compound such as permanganate or hydrogen peroxide, or free-oxygen itself, or in the form of atmospheric air.

The temperature at which the sour oil-agent-oxygen-sulfur are contacted may be in general those temperatures used in conventional doctor treating, i. e., between about 50 and 175 F. It is to be understood that the treating temperature may be determined by the flash point of the particular sour oil charged to the process. Thus when operating with naphthas, temperatures on the order of 70 P. will be used; when operating with a kerosene, temperatures between about and F. may be used; and when operating with a high flash point material such as a high boiling furnace oil, temperatures as much as F. or higher may be used. Still another limitation on the contacting temperature may be color formation in the oil, e. g., some herosenes rapidly develop color bodies when exposed for prolonged times at temperatures above about 100 F. It is preferred to operate at about the maximum temperature permitted by the type of stock used in order to decrease the PbS conversion time. The PbS conversion time is very favorably iufluenced by increase in the temperature of the contacting zone.

The contact time needed in the contacting zone determined by the rate at which the simultaneous reactions take place. The sweetening reaction and the PbS conversion reaction generally have different rates; it is possible by adjusting the alkanolamine concentration, the percent excess sulfur and the contacting temperature to obtain essentially identical reaction times. At alkanolamine concentrations below about 2% the sweetening reaction is usually appreciably faster than the PbS con version reaction. As the concentration of alltanolaminc is increased the PbS conversion reaction rate increases while the sweetening reaction rate decreases. Apparently in the neighborhood of about 5% alkanolarnine, the sweetening reaction is definitely slower than the PbS conversion reaction. As has been mentioned previously, the amount of excess sulfur has a definite effect On the reaction rates. The contacting must be maintained for a time at least long enough to both sweeten the oil and to convert substantially all the PbS to the plumbite. it has been found that the conversion of PbS continues after the separation of the agent phase from the oil phase. Thus it is not necessary to carry out the conversion reaction completely in the contacting zone. Usually a completely regenerated agent will be recycled to the contact-- ing zone when the PbS conversion reaction has proceeded to about 95% of completion prior to separation of the agent phase from the oil phase.

Since the contacting time is influenced by (a) the percent excess sulfur, (b) the alkanolamine concentration and (c) the temperature, contacting time will be discussed in terms of varying only one of these factors. At a constant sulfur usage and agent composition the contacting time for obtaining a sweet product and a regenerated agent may be as much as 4 to 6 hours at a temperature of about 60 F.; at a temperature of about 150 F. the contacting time may be as short as about 10 minutes. Thus higher temperatures correspond to shorter contacting times.

At a constant temperature and fixed excess sulfur usage, lower alkanolamine concentrations, such as bciow about 2%, the necessary contacting time may be between about 1 and 2 hours at about 80 F. and 20% excess sulfur. At high alkanolamine concentrations such as about 20%, the contacting time may be between about 3 and 4 hours, i. e., the higher alkanolamine concentrations correspond to longer contacting times.

At constant temperature and agent concentration, larger amounts of excess sulfur decrease the contacting time. At no excess sulfur usage the sweetening time is essentially infinite. At about excess sulfur usage, the sweetening time at about 80 F. and 2% alkanolamine concentration is about 2 hours. At 50% excess sulfur the corresponding contacting time is about onehalf hour, i. e., the higher free-sulfur usages correspond to the shorter contacting times.

It is to be understood that the regeneration need not be carried out in the presence of the oil that is being sweetened. The sweet oil may be separated from the spent sweetening agent prior to regeneration of the spent agent. The regeneration may then be completed by contacting the spent sweetening agent with air for a time 'sufiicient to convert the PbS and thereby regenerate the agent. This method of operation is of particular value in the sweetening of naphthas wherein the relatively low temperature of contacting requires a prolonged contacting time in order to regenerate the agent, i. e., when using low concentrations of alkanolamine and relatively small amounts of excess sulfur. In this method of operation the sweetening agent, free-sulfur, free-oxygen and sour oil are contacted for a time sufiicient to complete the sweetening reaction. Some PbS conversion also takes place. The sweet oil is then separated from the spent agent and the spent agent contacted with air either at the temperature of the sweetening zone or at some higher temperature in order to speed up the regeneration until the PbS has been converted. The regenerated sweetening agent is then recycled to the sweetening zone. it is pointed out that for some oils it. may be dificult to effect a clean separation of the sweet oil and the agent without very long settling times and for such oils there may be a definite saving in time and equipment size by simultaneously carrying out the sweetening and the PbS conversion.

The annexed drawing which forms a part of this specification shows an illustrative embodiment of one particular method of utilizing the process of this invention. It is to be understood that the drawing is schematic in nature and many items of process equipment have been omitted since these may be readily added thereto by those skilled in this art.

In the drawing sour oil from source 11 is passed by Way of line 12 into heat exchanger 13. Herein the sour oil is a heater oil boiling between about 330 and 570 F. and has a mercaptan number of 65. derived by distillation from a high sulfur Texas crude. Herein the sour oil is substantially HzS-free and no prewash with aqueous caustic solution is carried out. When the sour oil contains appreciable amounts of H28 it is desirable to avoid loss of the caustic in the agent by prewashing the sour oil with aqueous caustic solution.

The sour oil is raised in heat exchanger 13 to a temperature high enough to provide a contacting zone temperature of about 130 F. The hot sour oil is passed from heat exchanger 13 into line 14. A small amount of the hot sour oil is withdrawn from line 14 and is passed by way of valved line 16- into sulfur drum 17. Sulfur drum 17 is a vessel filled with elemental sulfur such as flowers of sulfur. The hot sour oil dissolves some of this sulfur and the free-sulfur containing oil is passed from sulfur drum 17 by way of valved line 18 back into line 14 where it meets the remainder of the hot sour oil. In this illustration sufiicient free-sulfur is dissolved to have present in the sweetening zone about 30% more This sour oil is the run proceeds the addition ofsweeteningagent will be limited to makeup quantities. The amount of sweet-' ening agent is at least enough to form a separate sweetening agent phase and may be between about'l and 20 volume percent based on sour oil. In this illustration 4 volume percent of sweetening agent is used. The sweet ening agentconsists of (a) doctor solution composed of about 12% of free sodium hydroxide and about 2% of PbO and (b) 2.5 volume percent of triethanolamine.

Air from source 26 is passed by way of line 27' into line 23. The amount of air present must be at least enough to oxidize the PbS formed in the reaction, i. e., 2 mols of free-oxygen per mol of PbS formed. More" than this amount is desirable.

The sweetening agent and the air in line 23 are introduced into line 14 at a point beyond the entry of the free-sulfur containing oil. The sweetening agent, air, sour oil and free-sulfur are introduced into reactor 28.

Reactor 28 is a vertical cylindrical vessel provided with a vent 29 and a motor-driven stirrer 31. The stirrer in this illustration is provided with three turbine blades. In order to improve agitation reactor 28' is provided with horizontal baflles 32a and 32b.

Although a mechanically agitated reactor is shown herein, it is to be understood that other methods of ob taining intimate contacting may be used, e. g., the reactor may be agitated with air. Also, an orifice mixer which provides a sufiicient contacting, time may be used.

The contents of reactor 28 are maintained at a temperature of about F. for 30 minutes in order to insure sweetening and substantially complete conversion of the' PbS. Sweet oil. andagent are withdrawn at a trap-out point near the top of reactor 28 and are passed by way of line 34 into separator 36. Separator 36 is a substantially horizontal cylindrical vessel providing suflicient settling time for the formation of a separate agent phase and an oil phase. Separator 36 is provided with a vent 37 for the withdrawal of excess air.

The lower agent phase is withdrawn from separator 36 by way of line 39. Normally the agent from line 39 is recycled to reactor 28 by way of lines 23 and 14. The conversion reaction results in the formation of water and sodium sulfate which dilute the agent. Periodically the agent is withdrawn from the system by way of line 39 and valved line 41.

The oil phase is withdrawn from separator 36 by way of line 44. This oil phase contains a very slight amount of occluded agent. The occluded agent may be removed from the sweet oil by either water Washing or by coalescing. Herein the oil phase is passed from line 44 into coalescer 46.

Coalescer 46 is a vertical cylindrical vessel provided with glass wool. Instead of glass wool, coalescer may be filled with crushed rock, sand or rock salt. Sweet hazefree product oil is withdrawn from the top of coalescer 46 and is passed to storage not shown by way of line 48.

The agent separated in coalescer 46 is withdrawn from the bottom thereof by way of line 51. This agent may be recycled to reactor 28 by way of valved line 52, line 39, etc.; or it may be withdrawn from the system by way of valved line 54-.

The agent withdrawn by way of lines 41 and 54 is preferably treated to recover the triethanolamine and the lead content. Conventionally the lead may be precipitated by treatment of the agent with hydrogen sulfide and oxidation of the PbS to PbO. The triethanolamine may be recovered from aqueous solution by fractional distillation. It is to be understood that the embodiment described above is merely one illustration of the use of the process of this invention in the sweetening of a sour hydrocarbon oil. Many variations of the above will be immediately apparent to those skilled in the doctor sweetening art.

The results obtainable with the process of this invention are illustrated by experimental data set out below;

All the experiments described hereinafter were carried out as follows: The contacting zone consisted of a 3- necked glass flask with a capacity of 2 liters. The flask was provided with a motor-driven stirrer, a thermometer and an electrically heated jacket. The sides of the flask were creased to improve agitation. One liter of HzS-free sour oil was charged in each run. Twenty ml. of sweetening agent was used in each run. Except when indicated otherwise, the agent consisted of (a) doctor solution containing 11% NaOH and 1.8% Pb() and (b) the triethanolamine (hereinafter designated TEA). Unless otherwise indicated, all the experiments were carried out at 90 F. The experiments were carried out by adding the sour oil and the agent to the flask in that order. Stirring was begun immediately after adding the sour oil. After the initial contact of sour oil and a ent, the desired amount of free-sulfur was added to the flask in the form of a 1% solution in xylene. Air was bubbled through the flask from the time of agent addition. The stirring was continued until both the sweetening reaction and the PbS conversion reaction were completed. The stirrer was then stopped and the contents of the flask settled for about 30 minutes, after which time the lower agent layer was separated. The product oil was dehazed by passage through a filter paper coalescer or by Water washing followed by dehazing through a filter paper coalescer.

For purposes of comparison runs were made according to conventional doctor processing, i. e., in the absence of added TEA.

In the runs using agent the course of the run was (ll immediately the black precipitate of PbS was formed; (2) as the contacting with air continued the black precinitate gradually disappeared and the agent solution regained its normal clear tan color.

Periodically a sample of the contents of the flask was withdrawn and the dehazcd oil tested for sweetness. The absence'of PbS particles clearly indicated the completion of the PbS conversion reaction. it was found that the agitation could be discontinued when about 904. 5% of the PbS had been converted: the remainin PbS was complctelv converted during the 30-minute settlintt period.

In Table T are presented comparative data showing the effect of variation in amount of excess sulfur and TEA concentration. Runs 1-5 were carried out using a kerosene boiling between about 340 and 513 F. which had a mercaptan number of 16.

in these runs the contacting temperature was 90 F. and 2 volume percent of agent was used.

Runs 1d, 2d and 30, which are examples of conventional doctor treating, show that no detectable amount of PbS conversion was obtained in the absence of TEA even though a sweet oil was obtained. These runs further show the conventional decrease in sweetening time as the percent excess sulfur is increased.

Runs 1, 2 and 3 clearly show the adverse effect of increasing TEA concentration on the sweetening time, at constant excess sulfur usage.

Runs 1, 2 and 3 clearly show the beneficial effect of increasing TEA concentration on the time needed to convert 9095% of the PbS formed. It is pointed out here that the times given are cumulative, i. e., the longer time represents the total time of contacting the oil and the agent.

Runs 10, 2c and 312 show the more normal situation wherein the sweetening time is shorter than the PbS conversion time. In these runs the oil was found to be sweet to the doctor test in the times shown even though the contacting zone still contains'considerable amounts of PbS. Run 10 shows that after 60 minutes the oil was sweet and that an'additional 60 minutes of agitation in the presence of air was needed to complete the PbS conversion reaction.

TABLE I Time, Minutes, Sulfur, Agent, to Obtain- SweetOil, Run No. Percent VPereent Cu Strip,

Excess TEA No.

Sweet PbS Con- Oil version 10 5.0 240 75 0 l0 3. 5 240 0 10 2.0 60 120 1 10 None 50 C) 1+ 20 5. 0 240 ca. 60 0 20 3. 5 120 60 (l 20 2.0 50 90 2 20 None 40 2 30 5.0 40 0 30 2.0 15 75 l 30 0.0 15 2 No conversion.

Runs 1a, 2a and 3:: illustrate situations where sweetening reaction was slower than the PbS conversion reaction. In these runs the PbS precipitate was formed immediately after the addition of the agent to the sour oil and at the time indicated all the PbS had disappeared; however, the oil was still sour to the doctor test. Additional contacting was necessary after the PbS had disappeared in order to obtain a sweet oil.

In the case of the conventional runs, 1d, 2d and 3c, the phases were separated only with difliculty due to the formation of black strap. However, in the runs using sweetening agent, the two phases separated very cleanly and the sweet oil had a barely perceptible haze.

Run 4 This run was carried out in the manner similar to Runs 1-3 except that the separated agent phase was used to contact a fresh portion of sour oil, i. e., conventional recycling procedure was simulated. Run 4d shows that sweetening agent can be reused at least four times with no loss in etficiency and essentially no loss of plumbite. All the runs are at a 2% concentration of TEA in the agent. The results of these runs are presented below:

Time, Minutes, Sulfur, to Obtain Available Run No. Percent PbO,

Excess g./100 ml. Sweet PbS Gun- Oil version 20 50 90 1 8 20 50 90 1 8 20 50 90 l. 8 10 60 1 8 1O 60 120 l 6 The PhD concentration in the agent was obtained prior to each use. The above runs indicate that until Run 4d there had been no loss of plumbite. These runs show that the process of this invention can be operated successfully on a recycle basis.

EFFECT ON COLOR Run 5 The eflect of the use of the sweetening agent of this invention on the color of the product oil was investigated in this run. Run 5a was carried out using sweet oil obtained in Run 1a. Run 5b was carried out using sweet oil obtained in Run is. Extensive investigation has indicated that the color stability on storage of a distillate in the heavier-than-gasoline boiling range can be predicted by means of a laboratory method. The results of this laboratory method are known as aged color. In this test 100 ml. of oil are maintained in an open beaker exposed to atmospheric orygen for 20 hours at 200 F. At the end of the 20 hours the Saybolt color of the oil is determined. This. color is the aged color ofthe oil. The results or these runs as presented below indicate essentially no adverse elfect on color and color. stabilityof the sweet oil.

Color, Saybolt EFFECT ON CORROSIVENESS The eflFect on the corrosiveness of the product oil was measured by means of the copper strip test in Runs 1-3. The copper strip corrosion is determined for an oil by immersing a copper strip in the oil for 3 hours at 212 F. The corrosiveness of the oil in this specification has been determined by the Bolt copper strip number technique. This technique is described in the August 9, 1947 issue of the Oil and Gas Journal. In this method the number is assigned to a perfect strip, i. e., equal to a strip prior to being used in a test. The higher the number assigned to a strip after the test, the more corrosive the oil.

The results of the corrosivity test as presented in Table I show that the copper strip number is improved with increase in TEA concentration and that in any case the oil produced by the process of this invention is at least as good in this regard as oil from conventional doctor treating.

Run 6 In this run there was used a heater oil boiling between 332 and 560 F. having a mercaptan number of 64. These tests were carried out using 10 volume percent of doctor solution or 10 volume percent of agent based on oil. One hundred percent excess sulfur was used in each test and the contacting temperature was 120 F. The times needed for obtaining a sweet oil and for PbS conversion were noted at various TEA concentrations. In this run comparative information was obtained on the burning quality of the heater oil.

It has been found that sleeve-type burners in domestic heating installations are most markedly affected by the presence of deposits formed during the burning of the oil. The Jungers burner is an example of an extremely sensitive sleeve-type burner. Because of this sensitivity the Jungers burner has been adopted by many refiners as a standard test burner for determining the burning quality of domestic heating oils. A full scale test using the Jungers burner involves the burning of many gallons of oil and many days of operation. A simple laboratory procedure has been developed which adequately predicts the results obtainable in the full size Jungers burner test. This laboratory method is known as the steel dish deposit test" or steel dish gum test.

The steel dish deposit test is carried out as follows: An 188 stainless steel dish is maintained at a temperature of 500 F. by means of a hot plate. The dish is saucershaped and has the following dimensions: Outside diameter, 2 inches; thickness at the edge, f inch; thickness at the center of the dish, inch. The depression in the dish corresponds :to a section of a sphere. The dish is provided with a thermocouple which permits the temperature of the dish to be measured. The dish i placed on a hot plate, the temperature of which is adjusted to maintain the dish at about 500 F. The oil to be tested is dripped at a substantially constant rate onto the dish. The rate of evaporation of the oil from the dish should be substantially equal to the rate of addition of the oil to the dish, i. e., the dish always contains a film of liquid oil. A 400 ml. sample of oil is used in each test and the oil is added dropwise to the dish at a rate of about 1 ml. per minute. At the completion of the test the dish is removed from the hot plate and allowed to cool. The

1:0 difference in the weight of the dish before and afiter the test is called the steel dish deposit.

A large number of tests on many difierent oils have been made and it has been found that an oillwhichi gives a steel dish deposit of 10 mg. will operate satisfactorily in a Jungers burner.

The results of these tests are shown below:

Time, Minutes, to Agent, V Obtain-- Burner De- Run No. Percent posits, Steel TEA. Dish Sweet Oil PbS Conversion *No conversion.

The effect of operating at high temperature was investigated using a heater oil having a mercaptan number of 16. The tests were carried out at a temperature of F., at a 50% excess sulfur usage and a 10% agent usage. The results of these tests are presented below:

Time, Minutes to 0b- Agent, V taiu Run N0. Perlient Sweet Oil PbS Conversion 7a.-. 2 30 10 7b- 1. 5 13 13 7C 1 15 25 7d None 10 30 These tests indicated that for this particular heater oil at this temperature essentially complete sweetening and regeneration can be obtained simultaneously at a TEA concentration of 1.5%.

It is noteworthy that even though at this very high temperature it is possible to regenerate the doctor solution without the use of TEA, the presence of 1.5% of TEA permitted regeneration to be carried out in less than onehalf the time with very little increase in sweetening time, Thu-s it is indicated that over the entire range of temperatures and excess sulfur usages normally utilized in conventional doctor treating, a definite improvement can be obtained by substituting the sweetening agent of this invention for conventional doctor solution.

Thus having described the invention, what is claimed is:

1. A doctor sweetening process which comprises contacting a hydrocarbon oil which contains an amount of mercaptans at least sufficient to render said oil positive to the doctor test, in the presence of free-sulfur, in an amount appreciably in excess of the theoretical amount needed to convert said mercaptans to disulfides, and freeoxygen, with doctor solution containing between about 0.5 and 50 volume percent of an alkanolamine containing not more than 3 carbon atoms in each alkyl group for a time at least suflicient to convert essentially all of said mercaptans to disulfides and separating a doctorsweet oil from said solution.

2. The process of claim 1 wherein said free-oxygen is present in an amount at least sufiicient to oxidize the PbS formed in the sweetening reaction and said contacting is continued for a time at least sufiicient to convert substantially all of said PbS.

3. The process of claim 1 wherein said amine is a monoethanolamine.

4. The process of claim 1 wherein said amine istriethanolamine.

5. A process which comprises (A) contacting a sour petroleum distillate boiling in the heavier-than-gasoline range With between about 1 and 20 volume percent, based on distillate, of a sweetening agent comprising (a) from about 0.5 to 50 volume percent of an ethanolamine and (b) the remainder essentially conventional doctor solution, in the presence of (i) between about 5 and 100% in excess of the theoretical requirement of free-sulfur and (ii) at least a suflicient amount of free-oxygen to convert substantially all the PbS formed in the process, at a temperature between about 50 and 175 F. for a time at least suflicient to substantially sweeten said distillate and to convert substantially all of the PbS formed in the process, and (B) separating a substantially sweet distillate from a substantially regenerated sweetening agent phase.

6. The process of claim 5 wherein the agent phase of step (B) is recycled for reuse in step (A).

7. The process of claim 5 wherein said free-sulfur is present in an amount between about 10 and in excess of the theoretical.

8. The process of claim 5 wherein said ethanolamine concentration is between about 1 and 4%.

9. The process of claim 5 wherein the temperature is between about and 150 F. and the contacting time is between about 6 hours and 10 minutes, the longer times an alkanolamine containing not more than 3 carbon atoms in each alkyl group and between about 1 and volume percent, based on doctor solution, of said amine is present.

References Cited in the file of this patent UNITED STATES PATENTS Fischer June 24, 1930 Morris Jan. 2, 1945 

1. A DOCTOR SWEETENING PROCESS WHICH COMPRISES CONTACTING A HYDROCARBON OIL WHICH CONTAINS AN AMOUNT OF MERCAPTANS AT LEAST SUFFICIENT TO RENDER SAID OIL POSITIVE TO THE DOCTOR TEST, IN THE PRESENCE OF FREE-SULFUR, IN AN AMOUNT APPRECIABLY IN EXCESS OF THE THEORETICAL AMOUNT NEEDED TO CONVERT SAID MERCAPTANTS TO DISULFIDES, AND FREEOXYGEN, WITH DOCTOR SOLUTION CONTAINING BETWEEN ABOUT 0.5 AND 50 VOLUME PERCENT OF AN ALKANOLAMINE CONTAINING NOT MORE THAN 3 CARBON ATOMS IN EACH ALKYL GROUP FOR A TIME AT LEAST SUFFICIENT TO CONVERT ESSENTIALLY ALL OF 